German patent document DE-U-86 20 385 describes a writing instrument of the aforedescribed type having a reserve chamber which, in the usual orientation of the instrument for writing purposes, is located above the supply chamber. The valve element of the refilling valve is connected with a plunger which is actuatable at the end of the reserve chamber opposite the end of the instrument provided with the writing tip or nib. By depressing this end of the plunger, the valve element is displaced from its normally closed position into an open position and then subsequently can return to its closed position.
With the known writing instrument of this patent document, in the closed position of the refilling valve, the volume of the supply chamber is exclusively effective. The supply chamber can be so constructed that the greatest amount of air possible is permitted via the equalizing capacity of the capillary system, to dominate the flow of ink from the tip. This ensures that nonuniform ink flow is avoided and ragged writing is prevented.
When the supply chamber is emptied in the course of writing, it must be refilled with ink from the reservoir chamber.
The writing instrument of DE-U-86 20 385 has the drawback that after the supply chamber has been refilled from the reservoir chamber, refilling of the reserve chamber with ink is not possible and thus the instrument must be discarded when the ink in both the supply chamber and the reserve chamber has been fully consumed.
U.S. Pat. No. 2,646,777 discloses a refillable writing instrument in which the supply chamber at the end opposite that provided with the pen point, is provided with a piston pump which can allow a suction tube projecting from the supply chamber to be operated. To refill the supply chamber, the suction tube is immersed in ink in an ink vessel and by up-and-down movement of the instrument, the piston pump is actuated.
This system has the drawback that, during refilling, the pressure rise in the supply chamber causes ink in the flow regulator to feed through the pen point or tip and contaminate the fingers of the user and the exterior of the instrument. Overfilling of the supply chamber and the ink compartment in the flow regulator can readily occur with this system so that the writing produced by the instrument can be ragged. Finally, the instrument is difficult to manipulate and, because of the suction tube projecting from the supply chamber, required that an additional protective cap or sleeve be provided.